Page 192 - Photoshop for Lightroom Users – Scott Kelby 2nd Edition

Tip: Sharpening Previews
When you use the Unsharp Mask filter, you get two previews of your sharpening: (1) you see the effects in your image right onscreen as you drag the
sliders, and (2) you see a zoomed-in preview of how the sharpening is affecting your image in the small preview window inside the dialog itself. Click-and-
hold inside this window to get a before (unsharpened) view of your image; release the mouse button to see the after.

Smart Sharpen Filter: Smarter Sharpening (With Smart Sharpen)
This one is aptly named—it’s a sharpening filter that uses a better mathematical algorithm than Unsharp Mask (which, by the way, has been in Photoshop
since version 1.0), which lets you apply more sharpening with less of the bad stuff associated with it (increased noise, halos that appear around the edges of
objects, or little specks or artifacts in the sharpened image). So why does anyone even use Unsharp Mask? Because it’s the classic sharpening, it has been
around forever, people know how to use it, and people don’t like change (even if better sharpening, with more control, is just one spot up in the Sharpen
menu).